Foam extrusion technology is well-known in the art. Traditional expanded polystyrene technology has existed since the early 1950's, and is discussed, for example, in U.S. Pat. Nos. 3,151,192 and 3,431,164. Uses for low density foam extrusions include foam insulation and food packaging.
Although many foamed articles comprising engineering thermoplastics such as polycarbonates, polyesters, polyamides, polyolefins, polyphenylene ethers, as well as compositions of the foregoing with other thermoplastics such as polystyrenes, are known, it is not generally a part of the foam extrusion art to produce flame retardant structures from them.
For example, in U.S. Pat. No. 4,454,087, foamable compositions are described which may be comprised of styrene, polyethylene, polypropylene, polycaprolactam and the like. There is no apparent mention of the use of flame retardants in the compositions or of the flame retardant characteristics of the articles themselves.
In U.S. Pat. Nos. 4,661,302; 4,705,811 and 4,734,441 processes and compositions relating to foamable polystyrene resins, which may include a polyphenylene ether expansion aid and/or a phosphate plasticizer, are described. Again, there is no apparent mention of the use of any specific flame retardants in the compositions or of the flame retardant characteristics of the articles themselves.
In U.S. Pat. Nos. 4,579,710; 4,579,873; 4,579,874; 4,579,878; 4,587,271; 4,594,208; 4,598,100; 4,598,101 and 4,598,104, there are described foamable thermoplastic compositions which may be comprised of resins selected from the group consisting of solvent imbibable polyetherimide, polycarbonate and polyphenylene ether resin in combination with polystyrene resin. The foamed compositions are described as having a density of less than about 20 lbs./cu.ft. Although the patentees in these disclosures mention that the resulting foam compositions are inherently flame resistant and low in smoke generation, the only exemplified composition exhibiting any flame resistance is of a polyetherimide, which is inherently flame retardant.
Finally, in British Patent No. 1,479,292, compositions are described which are comprised of a minor amount of a foaming agent in conjunction with a thermoplastic resin. The thermoplastic resin can be selected from the group consisting of an aromatic polycarbonate, a polyester, and a polyphenylene ether or a mixture thereof with a styrene resin. The patent mentions that pellets produced from the described compositions are directly moldable to produce a structural foam article. The patent also mentions that the described foamable compositions may contain conventional flame retardants, such as, for example, halogenated compounds or compounds containing phosphorous and/or nitrogen. No flame retardant compositions, or even compositions containing a flame retardant, are exemplified.
A need therefore, continues to exist to produce low density foam articles from thermoplastics which are flame retardant. Methods to make the same, and the foamed articles themselves, have now been discovered and are the subject matter of this invention.
It is therefore an object of the present invention to provide flame resistant, preferably flame retardant, low density extruded foam articles or articles molded from expandable foam beads.
In particular, it is an object of the present invention to provide low density foam insulation, preferably in the nature of foam boards, for the building and construction industry which have satisfactory flame spread and smoke development characteristics according to Steiner Tunnel (ASTM E-84) Flammability Tests.